This invention relates to a cable winding drum and more particularly to a cable winding drum for closing a power sliding vehicular door.
Power sliding doors for automotive vehicles such as minivans have seen recent popularity. The use of automatic doors is a great convenience for handicapped people, for young children and for other people who have their hands filled for example with groceries.
The use of pull cables have been found to be an expeditious mechanism to both open the door and close the door. When the cable is used to close the door, more torque is need for the cable to close the door against the resisting forces of the seals and door latch. Thus, it is greatly desired to increase the torque exerted by the cable winding drum to overcome the seals and latch mechanism without excessive forces exerted on the cable that may otherwise decrease the durability of the cable.
In accordance with one embodiment of the invention, a cable winding drum for closing a vehicle power sliding door includes a first helical outer surface with a first radius about an axis of rotation for taking up cable at a first rate when closing the vehicle door. A second outer elliptically contoured helical surface is tangent with the first helical surface in proximity to a major axis of said second outer elliptically contoured helical surface. The take-up drum when in full closed position has the cable extended out on the second outer elliptically contoured helical surface in proximity to its minor axis at a point substantially closer to the axis of rotation than the first helical outer surface.
Preferably, the second outer elliptical contour has an eccentricity of at least 0.5.
It is also desired that the second outer elliptical contour has its minor axis intersect the axis of rotation with the axis of rotation interposed between the elliptical contour and the center point for the elliptical contour.
In accordance with another aspect of the invention, a first outer surface of the drum has a general first radius about the axis of rotation for taking up cable at a first rate. A second outer facing smoothly contoured surface has a greater bent section tangent to the first outer surface with a decreasing radius with respect to the the axis of rotation and a less bent section of the second outer facing smooth surface about the drum, the maximum tension force of the cable is misaligned and at a different point of the cable from the maximum bending force of the cable. It is preferred that the second outer facing smooth contoured surface has an elliptical contour.
In this fashion, the cable have its peak bending forces and peak tensile forces located at different locations along the cable thus lowering the peak combined force load on the cable which increases its durability.